This invention relates to a turbojet powerplant for aircraft applications which is provided with a heat exchanger.
More particularly, this invention relates to a turbojet powerplant with at least one compressor, at least one combustion chamber, a high-pressure turbine and a low-pressure turbine.
A great variety of designs of turbojet powerplants is known in the prior art. The objective of the technical development in this field is the improvement of efficiency to achieve, among others, a lower fuel consumption. The associated development effort focuses on the continuous improvement of the efficiency of the individual components. However, the related optimisation measures cannot be progressed ad libitum, in particular with respect to the cost-to-profit-ratio.
In a broad aspect, the present invention provides a turbojet powerplant of the type described at the beginning which combines simplicity of design and safety of operation with improved efficiency and low specific fuel consumption.
It is the principal object of the present invention to provide remedy to the above problematics, with further advantageous aspects of the present invention being cited in the subclaims.
The turbojet powerplant according to the present invention, therefore, provides an arrangement in which a heat exchanger is located between the compressor and the combustion chamber, in which at least one hot-gas line is branched off from an area downstream of the high-pressure turbine and is connected with the heat exchanger, and in which at least one cold-gas line connects the heat exchanger with an area upstream of the low-pressure turbine.
The turbojet powerplant according to the present invention has a variety of merits.
The provision of a heat exchanger according to the present invention enables the compressed gas supplied to the combustion chamber to be heated additionally. By virtue of this additional energy input, a correspondingly smaller amount of fuel-supplied energy is needed in the area of the combustion chamber. This effects a considerable reduction of the fuel consumption, with the output power of the turbojet powerplant remaining unchanged. The take-off of hot gas from an area downstream of the high-pressure turbine ensures that the temperature of the hot gas is high enough to supply a sufficient amount of heat to the heat exchanger.
The combined effect of the features according to the present invention enables the specific fuel consumption (SFC) to be reduced between 2 and 4 percent. This reduction of the specific fuel consumption is independent of any other measures for the optimisation of the turbojet powerplant.
In a particularly favourable development of the present invention, the heat exchanger is designed such that it is capable of flowing the entire amount of the air discharged from the compressor. This ensures that the entire compressed air or the entire compressed gas, respectively, will be heated correspondingly as it flows through the heat exchanger.
The heat exchanger in accordance with the present invention is preferentially of the counter-flow type. This type provides for favourable and safe operation. In a further advantageous development, the heat exchanger is designed as diffuser on the side of the compressor air, this design providing for partial compensation of the heat exchanger pressure loss through heat transfer. This effect is augmented in that the gas exiting from the compressor is forced to pass the heat exchanger, as described above.
In a particularly favourable embodiment of the present invention, the hot gas is discharged to the high-pressure turbine via holes in the leading edge areas of a first row of vanes and is supplied to the hot-gas line via associated lines. Upon entry in the vanes, the hot gas is decelerated and ducted radially outward into a first compartment (annulus). In a favourable arrangement of the present invention, the hot-gas lines which supply the hot gas to the heat exchanger are flanged to this annulus. Apparently, the present invention may be implemented with several hot-gas lines and with several cold-gas lines. Accordingly, the purpose of the first annulus is to combine the individual hot-gas flows from the vanes.
For the protection of the first annulus against too high temperatures, heat shields are provided on its interior side.
Preferentially, for the return of the gas (cold-gas) issued in the area of the heat-exchanger, a second annulus is provided to which the cold-gas line is joined. This second annulus (annular duct) serves the uniform circumferential distribution of the returned cold gas. Again, heat shields are provided to prevent the casing of the second annulus from overheating.
From the second annulus, the cold gas flow will preferentially flow into vanes of the low-pressure turbine which are open to this second annulus. Subsequently, the cold gas exits from the interior of the vanes through openings at the trailing edges. As the gas passes through the vanes, a further heat transfer takes place between the working gas and the cold gas via the walls of the vane airfoils. Said heat transfer causes the temperatures to equalise to some extent, this effect resulting in a more uniform flow profile in the low-pressure turbine. In a favourable arrangement, the exit slots or exit openings at the trailing edges are designed as nozzles.
To ensure an aerodynamically and thermally optimum gas flow through the heat exchanger, it may be advantageous to supply the hot gas from the hot-gas lines to the heat exchanger via local hot-gas chambers. Preferentially, these hot gas chambers are connected to a hot-gas annulus from which the hot gas is fed into axially and radially arranged plates. In these plates, the hot gas flows forwards in the counter-flow direction, thereby transferring heat to the compressor airflow which passes in the opposite direction. In the front portion of the heat exchanger, the cooled-down hot gas (accordingly referred to as cold gas in this application) is collected in a cold-gas annulus and passed from there to the cold-gas lines via local cold-gas chambers. The local hot-gas chambers or the local cold-gas chambers, respectively, serve the conduction of the respective gas volume into the individual hot-gas lines or cold-gas lines, respectively.
In accordance with the present invention, then, the hot gas to be supplied to the heat exchanger is taken off downstream of the high-pressure turbine and, after having passed through and being cooled down in the heat exchanger, is fed as cold gas flow to the working gas upstream of the low-pressure turbine. This provides for a very advantageous, compact design of the turbojet powerplant on the one hand and a low total mass of the arrangement on the other. The combined effect of all these features provides for a reduction of the specific fuel consumption.